Method and device for conveying a pre-printed striplike recording medium in a printing device

ABSTRACT

A method and a device for controlling a drive unit which conveys a striplike laterally pre-printed recording medium, whereby a sensor is sensitized with respect to a regularly re-occurring mark of the recording medium. The recording medium is continuously scanned by the sensor during the printing operation and the speed at which the recording medium is conveyed is adjusted according to scanned signals from the sensor.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus fortransporting preprinted web-shaped recording media, particularly ofcontinuous form paper, in an electrographic printing device, inparticular. Paper, film material, labels or other materials can be usedas the web-shaped recording medium.

The greatest variety of paper grades are employed when printing paper.What is referred to as margin-perforated paper is mainly employed in theelectrographic high-performance printer field with printing outputs ofmore than 40 pages per minute. This paper has lateral holes at itslongitudinal edges for transport and for monitoring the position of thepaper. It is thereby driven by sprocket tractors that engage into thelateral transport holes. This paper often also has transverseperforations along which the individual pages are separated from oneanother.

The margin perforation is particularly employed when processingpreprinted paper. Given this paper, the information subsequently appliedin the electrographic printer, for example data that are printed on apre-printed form, should come to lie as exactly as possible atpredetermined locations of the pre-print. The form can have beenpreprinted by a printing device of another construction, for instance byan offset printer, or by an identical electrographic printer. Forpositionally exact printing, the position of the paper web in theconveying direction must be exactly adjusted to or, synchronized withthe drive thereof or, the movement of the photoconductor drum.

For exact positioning of such paper, the first page of the paper web isplaced exactly at a specific position with respect to the sprockettractors. A page start mark of the pre-print or, of, the transverseperforation thereby exactly prescribes the beginning of the page. Allfurther pages are automatically exactly positioned due to theconstrained guidance by the tractor sprocket when the first page wasproperly inserted.

The feed of the perforated paper usually occurs in a specific gridcorresponding to the hole spacings, for example in a {fraction (1/2+L )}inch grid or in a {fraction (1/6+L )} inch grid. The paper web is thennot moved continuously but step-by-step by a multiple of the gridspacing.

There is frequently also the demand in the high-performance printingfield to be able to employ roll paper that does not comprise such marginperforations in printers for continuous-form paper. Both economic aswell as ecological considerations contribute to this demand. Whenprinting margin perforated paper, namely, a processing step wherein themargin strips are removed from the printed page is necessary, wherebythe waste that thereby arises must be disposed of.

For example, WO 95/19929 A1 discloses a printer that is suitable forprocessing roll paper without margin perforation. A first seating edge,which prescribes the lateral position of the paper, as well asstabilization rollers, an under-pressure brake and a roller arrangementwith a loop-drawing means are provided in this printer for the exacttransport of the paper.

Even though continuous form papers both with and without marginperforation can be fundamentally processed with such a device, problemsarise when printing forms. When one wishes to process pre-printed paperwith such a printer, then no direct allocation of the pre-printed areato the information to be subsequently printed is possible. As a resultthereof, the information to be subsequently printed cannot be fittedinto the pre-print in positionally correct fashion.

Causes of mispositioning are, for example, fluctuations in the paperlength that derive from different ambient temperatures or differentdegrees of moisture of the paper web. Such fluctuations can amount to upto a few millimeters per page. Deviations in the print image on thisorder of magnitude are not acceptable when printing forms.

Added thereto given tractor-less friction drives is the problem that thetransport precision in the feed direction cannot always be adhered to.For example, slippage between the drive drum and the paper web ormanufacturing tolerances of the drive mechanism can contribute thereto.

DE 19 37 699 A likewise discloses a friction drive for data printers. Asensor that recognizes a pre-printed mark at the edge of the form isprovided given this drive. A reallocation of the line height to theprinting location is undertaken with the sensor result with therespective start of the form. What is disadvantageous about this driveis that a mark adapted to the sensor must be pre-printed at a specificposition of the form so that the control function can be implemented.

CH 608 904 A5 teaches an apparatus with which it is possible to write arunning band of forms with individual data. For this purpose, a sensoris provided, which detects a particular printed feature in the forms andthen triggers the print process within a particular field in the forms.The disadvantage of this apparatus is that, on the one hand, the featureon the forms must have a particular design, for instance a rectangularshape, in order to be reliably detected by the sensor. On the otherhand, the measurement accuracy of the sensor strongly depends on whichrecording medium is used. In particular, the contrast of a mark relativeto the background (e.g. to a paper surface) can differ significantlyfrom one recording medium to the next (e.g. given different types ofpaper).

DE-A-1937699 teaches a method and an apparatus for controlling a driveassembly for a web-shaped recording medium, which has been preprinted inpages in which a sensor is provided for scanning the recording medium.DE-A-2526190 as well as U.S. Pat. No. 4,994,975 and JPA-5902068 teachsuch methods. It is common to all these methods that they stipulatespecific characteristic attributes of the mark, for instance withrespect to the color of the mark or the contrast between the mark andits background surface, in order to be able to employ the respectivelyprescribed sensor. Therefore, the recording medium must be printed in aparticular way.

De-A-19631747 teaches an optoelectronic sensor device, which works inconjunction with a light source, for detecting a marking that is knownin advance on a web-shaped recording medium in electrographic printingor copying devices as well as a device for controlling the sensordevice. It is provided there that the type of measurement method, orrespectively, the selection of a required light source, is decideddepending on a known mark that is provided on the recording medium.

SUMMARY OF THE INVENTION

It is an object of the invention to set forth a method and an apparatusfor controlling a drive for web-shaped recording media with whichunspecified preprinted recording media can be transported withpositional precision.

This object is achieved according to the invention by providing a methodfor controlling a drive assembly and an electrographic printer whichtransports a web-shaped recording medium that has been preprinted inpages. A recording medium is selected which has been preprinted withinformation arbitrarily in pages. The recording medium is scannedcontinuously by a sensor during print operation. A regularly recurringmark is selected from the preprinted information or from a surfacestructure of the recording medium. The sensor is sensitized to theregularly recurring mark of the recording medium by setting sensorparameters. A transport speed of the recording medium is regulated usingscanned sensor signals. A device for carrying out the method is alsoprovided.

According to a first aspect of the invention, in order to control adrive assembly that—in an electrographic printer, inparticular—transports a web-shaped recording medium that has beenpreprinted in pages, a sensor is sensitized to a regularly recurringmark of the recording medium by setting sensor parameters. The recordingmedium is continuously scanned during the print operation using thesensor, and the transport of the recording medium is regulated using thescanned sensor signals.

According to the invention, the selected recording medium can bepreprinted arbitrarily in pages. From the preprinted information or fromthe surface structure of the recording medium, a regularly recurringmark is selected, and the sensor is sensitized to the regularlyrecurring mark of the recording medium by setting sensor parameters.

In an advantageous exemplifying embodiment of the invention, the marksare selected from the preprinted information of the recording medium,and an optoelectronic sensor is used, in particular. The marks can belocated in the print-capable region of the printing device, or, in theregion of the placement of forms into which the printer printsindividual data. But it is also possible to use a surface structure,particularly a window cutout, as a mark. The method is therefore veryflexible. The printer can process arbitrary documents, sensitizing thesensor to the respectively appropriate or prescribed mark information.The mark is applied page by page, in particular, the information thereofbeing used to control the drive page by page.

To sensitize the sensor, the background information (color, structure,or the like) of the recording medium, on which the form is based, isfirst scanned before the mark is sought. An advantage of thisexemplifying embodiment is that the mark used for the sensitizationcorresponds precisely to the subsequent forms that are printed onsubsequent pages.

In a second aspect of the invention, the sensitization occurs by meansof a measurement surface, which is moved automatically or manually fromthe sensor in an initialization procedure, so that the sensor can scanthe marks. For this purpose, either the sample of a currently preprintedmark, or a standardized measurement surface that represents standardizedmarks can be used. The measurement surface can be constructed as acolored surface (opaque copy) or as a transparent colored film. Tomeasure the background, a measurement surface can be provided whichcorresponds in particular to the recording medium that is to be inserted(e.g. to a particular paper type). In particular, a sample of therecording medium as a measurement surface can serve this purpose.

In a third aspect of the invention, the contrast between the mark andthe background on which the mark is printed is calculated. Severalalternative procedures are proposed for this. First, it is possible todetermine the contrast with the aid of the mark and/or using themeasurement surfaces. Alternatively, it is possible to determine themark and/or the background on the recording medium directly on therecording medium and to derive the contrast from this.

For sensitization and/or to detect the marks following the first markdetected, the recording medium is first transported with a first,predetermined speed, whereby a window within which the sensor signalsare acquired is prescribed, in particular a time window or a number ofincrements of a step motor. Synchronously with this process or at a timeoffset, it is checked whether the mark has been detected, or, wasdetected, within this window, and an error message is output when themark is not detected within the time window.

A control that is allocated to the sensor can also be fed characteristicdata about the mark from outside, particularly in the header area of aprint job.

The recording medium is first moved a particular length in the recordingdirection, in order to sensitize the sensor to the specific mark. If themark is not found during this forward motion, the recording medium issubsequently moved in the opposite direction. Several such cycles offorward-back movements can be executed, with an adjustment value beingchanged at the sensor after each cycle. Sensor parameters such asspectral sensitivity can be modified. The position of the sensor in thecoverage area can be modified, namely transverse to the transportdirection of the recording medium.

It is also advantageous to dispose the sensor such that it can be movedtransverse to the recording direction. The mark can then be located atan arbitrary point on the form. It is then possible to use the actualcomponents of the form themselves, such as text, graphics, or windowcutouts, as the marks. The sensor according to the invention can thus beadapted to the respective form contents in that it is sensitized to aselected item of information.

In a preferred exemplifying embodiment, the sensor can be colorsensitive in particular; the sensitization—that is, the setting ofsensor parameters—is performed to particular colors of the background,or respectively, of the mark. Alternatively or in addition, thesensitization of the sensor can be performed with respect to a geometricshape of the marks or with respect to the surface structure of therecording medium web. For instance, the marks can be notches that areprovided in the paper webs or window cutouts in the blank forms. Asensor setting value that is computed in the sensitization isadvantageously stored and reutilized for later measurements.

The sensitizing of the sensor is preferably performed in that the paperis transported at least once in or against the transport direction,during which process the evaluating unit checks if and when the sensordelivers a signal. It can be provided that at least one cycle of forwardand reverse movements be performed, and that after each movement or eachcycle, a setting value at the sensor is modified.

In an advantageous development of the invention, the front edge of thepreprinted web of the recording medium that is provided with marks isseated in an input region of the printer at a predetermined insertionmark. Next, the recording medium web is transported a predeterminedlength along a transport direction by a transport motor at a first,relatively low speed. During this process, a sensor scans apredetermined area of the paper and sends scan signals to an evaluatingunit. This evaluates the signals and checks whether they can beassociated with a predetermined mark. The transport length between twosuccessive marks is identified by the evaluating unit as the value for apage length. Finally, the print process is initiated at a second,relatively high transport speed and is controlled using the identifiedvalue for the page length.

The invention makes it possible that the drive for the recording mediumweb is synchronized to the page length even after a feed of one page.Therefore, position deviations of the web which arise due to impreciseinsertion of the paper web or elevated slippage between the drive andthe web are automatically compensated. The print process can then occurbeginning with the second page already. Maculature, i.e. excessunprinted paper, is thus largely avoided. The printing ensues withpositional precision in the blank with the first printed page already.

In particular, what is accomplished by the inventive start procedure isthat the print process can begin with the first page following the pagerequired for sensitizing the sensor.

The invention is particularly suited to application in a printing systemcomprising two structurally identical printers that are connected inseries, in which the second printer processes the paper web output bythe first printer online; that is, without a significant time delay. Inthis type of system, known as a twin printing system, the second printerprints the paper web output by the first printer optionally on the versoor on the same side, with a different color, for instance. The twoprinters can be provided with a tractor drive or with a tractorlessfriction drive for transporting the recording medium. During the printprocess, the second printer scans the marks printed by the first printerin order to regulate its processing speed in such a way that the printformats are superimposed exactly, or, that the printers worksynchronously to one another.

In a twin printing system such as this, it is particularly advantageousto adapt the measurement surface in the second printer precisely to theprint color of the first printer. If the first printer is capable ofprinting a limited number of print colors, a set of measurement surfacesthat are identical to the print colors of the first printer can be madeavailable in the second printer.

But the measurement surfaces can also be applied on the recording mediumas a gray value and/or as a stripe pattern by the first printer andscanned in the second printer.

The inventive procedure can be substantially automated. This rules outthe possibility of operator errors in the insertion of the web-shapedrecording medium into the printer, or, this makes it possible tocompensate such errors. The process only requires a small amount oftime, and so the effective printing time of the printer is high. Whenthe sensor is shifted using a motor drive, the degree of automation ofthe processes can be increased still further.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a printer with a tractorless paper drive,

FIG. 2 shows a section through a drive assembly;

FIG. 3 is a view of the drive assembly.

FIG. 4 illustrates a sensor arrangement;

FIG. 5 is a block circuit diagram of the control of the drive;

FIG. 6 is a flowchart of the control of the drive.

FIG. 7 shows a flowchart of the sensitizing of the sensor;

FIGS. 8a-8 e illustrate different variants for scanning measurementsurfaces;

FIG. 9 shows embodiments of measurement surfaces.

FIGS. 10a-10 b different variants for scanning a recording medium;

FIGS. 11a-11 b shows a scanning surface of a mark sensor.

The printer device represented in FIG. 1 draws a band-shaped recordingmedium (paper) from a paper input receptacle 1 or from a supply roll 11.In the roll operation, the paper web 5 is fed to a guide mechanism 2 viaa loop 12 and is then fed in a web precentering device 3 to frictiondrive rolls 4 along a seating edge. Next, it is drawn by a drive 8 viaan under-pressure brake 6, which is connected to a vacuum pump 7 thatgenerates the under-pressure. The paper web 5 is braked by theunder-pressure, increasing the tension of the paper web. The higher thetension is, the more stably the paper web 5 runs in the transportdirection A; that is, the less it slides out of the desired papertransport direction laterally. Following the under-pressure brake 6, thepaper web 5 passes through a stabilizing zone, which is formed ofseveral guide rolls 9 and a loop draw 10. The paper web surrounds theguide rolls 9 at least 180°, stabilizing the paper web laterally evenmore.

Before the paper web 5 is fed to a print assembly 14, a sensorarrangement 17 scans the paper optically. The sensor arrangement 17 islaid out such that it can scan the widest paper that can be processed inthe printer over its entire width. The width of the sensor arrangementis thus adapted both to the mechanical components for paper transportand to the parameters of the printing device 14 on the recording side,which determine the printable width. It is suited to the width of aphotoconductive drum 16, in particular. In the present exemplifyingembodiment, the processible paper width ranges from 6.5 inches (165 mm)to 19 inches (482.6 mm). Details of the sensor arrangement 17 aredescribed in DE-U-297 23 879 (internal file number 971101).

From the sensor arrangement 17, the paper web 5 is fed to a transferstation via a drive assembly 13. In this exemplifying embodiment, thetransfer station comprises a photoconductive drum 16, which works inconjunction with a corotron device 16 a. The photoconductive drum 16 ischarged with information by light in known fashion, a charge image beingthus applied. It then picks up a magnetized toner, which is transferredto the paper web 5 in the print transfer area. Next, the corotron device16 a discharges the corresponding area of the photoconductor drum again,so that this can be written with information again. The corotron device16 a operates in known fashion, as described in EP 0 224 820 B1.

In the illustrated example, the sensor arrangement 17 is arranged in theregion of the paper feed 15, though it can also be provided inside theprint assembly 14. The paper web 5 is transported in the paper transportdevice A.

FIG. 2 more closely shows the drive assembly 13 that is arranged in theregion of the print transfer station or, the photoconductive drum 16 ofthe electrographic printer.

At the drive roller 40, a roll arrangement 20 presses with theprescribed springing force. As a result, the paper that is beingtransported through between the rolls 40 and 20 is moved by the driveroller 40 by means of friction. The drive roller 40 is connected to thestep motor 41 via a toothed gear drive, in turn. The overall driveassembly 25 is flanged to a printer housing via the bearing block 44. Atthe bearing block 44, a common bearing axle 42 is borne by the ballbearing 43, the axle receiving the rotational motion of the drive roller40, on one hand, and making it possible for the drive elements to pivotabout the axis B, on the other hand. To enable the pivoting motion, thedrive components are mounted on a carrier plate 47, which is connectedvia a gas pressure spring 49 and via the bearing axle 42 to the bearingframe 44.

Threads 45 in the bearing frame 44 serve to receive fixing screws whichare led through the printer housing 18. The overall drive assembly canbe aligned within the printer housing via guide surfaces 46. The carrierplate 47 can be aligned in turn with respect to the bearing block 44, afirst adjustment screw 51 and a second adjustment screw 52, at which thestraight pins at the carrier side abut, being provided in the bearingframe 44.

The gas pressure spring 49 is connected to the carrier 47 by thethreaded connection 50 and to the bearing frame 44 by the threadedconnection 48. Carrier 47 and bearing frame 44 can be locked against oneanother using the lock mechanism 54.

A paper web which is inserted into the drive assembly 25 between thedrive roller 40 and the counterpressure roller 20 is led by a guideplate 53 to a paper sensor 55. The paper sensor scans the paper over theentire width of the printable area of the photoconductive drum, by whichprocess it is possible to detect the lateral paper edges as well aspotential margin perforations of the paper web. In the region of theprint transfer zone 5 of the print device, the paper is pressed by thespring-loaded pivot cheeks to the surface of the photoconductive drum 2.An electric corotron device 57, which is known per se, generates a highvoltage, by which the toner that is located on the photoconductive drumis drawn to the paper. Guide rollers 58 guide the paper further to amark sensor 59, which detects print or cut markers that may be presenton the paper web. Grounded electrical connections 61 (antistatic plates)dissipate electrical residual charges that may be present on the paper.

When paper with margin perforations is transported using the papertransport, the margin perforation can be scanned using a pin feed wheel60.

FIG. 3 shows the paper drive 25 in a three-dimensional representation.Specifically, the straight pin 66 that is installed at the carrier plate47 can be seen, which works in conjunction with the adjustment screw 52that is screwed into the bearing frame 44, as well as the screwconnection 50 of the gas-pressure spring 49.

Above the guide rollers 58, the paper is led by a guide surface 69. Inthis area, the scanning of the paper with the mark sensor 59 is alsoaccomplished. Furthermore, a seating rule 65 is provided in this area,which is used for the printer's start process. Newly inserted paperwhich has margin perforations is seated with the beginning of a page ata mark 65 a on the rule 65 (which corresponds to the page length); themargin perforation is engaged with the pin feed wheel 60, which has beenpivoted in; and the print process is initiated. The pin feed wheel 60 isa component of a sensor arrangement which is described more closely inFIG. 4.

In the transfer area, a drive motor 68 draws a corotron wirecorresponding to the width, which is to be printed, of the page from thecorotron wire cassette 57. The mark sensor 59 can be displaced along thebar 73 in direction E. The plate 66 covers the drive motor 41 and servesin particular for electromagnetic shielding. Corresponding to the frontbearing frame 44, a rear bearing frame 67 is also provided, which islikewise secured at the printer housing.

FIG. 4 shows the pin feed wheel sensor 85, which comprises the pin feedwheel 60. In the position illustrated, the pin feed wheel is swivelledout; that is, the pins do not project out over the paper guide plane 67.This pin feed wheel 60 can be swivelled in and out in direction F usingthe actuating lever 86. The pin feed wheel 60 is mounted on an axle 87,which likewise bears a toothed gearwheel 88. A magnetoresistive sensor91 detects impulses of the metal toothed gearwheels of the toothedgearwheel 88. These impulses can be unambiguously allocated to therotational movement of the pin feed wheel 60, so that the scanning ofthe margin perforation of the paper can occur, this running across thepaper plane 67 and engaging with the pin feed wheel 60. From theseimpulses, the speed of the paper web and its position in relation to thetransport grid of the drive mechanism can consequently be computed. Thesignals of the sensor 85 are therefore used as input signals for ananti-slip control of the paper drive. The sensor assembly 89 isconnected electrically to a device control (FIG. 5) for this purpose.

A second magneto-resistive sensor 92 detects whether the pin feed wheelsensor 85 is in the in or out position relative to the paper guide plane67. For this purpose, it acts in conjunction with the magnet 93 that ismounted on the guide surface 67. Using a stop mechanism 90, the overallpin feed wheel sensor 85 can be held in the in or out position,respectively.

FIG. 5 shows electronic components of the printer and their interactionwith the drive mechanism and sensor system. The drive assembly 13 has adrive control 100 via a shared data bus 112, which is connected to thehigher-ranking printer control 101. Operator instructions can be inputvia a control panel 105. The drive control 100 receives the signals ofthe paper width sensor 17, or, 55 via its interface 104. From these, itcomputes both the width and the type of the paper; that is, whether ornot there are margin perforations. The drive control 100 also receivesthe scanning signals of the pin feed wheel sensor 85 via its electronics103 and those of the mark sensor 59 via its electronics 107. From thesignals of the components 103 or 107, respectively, the speed of thepaper web 5 is computed in the drive control 100. The result is utilizedfor anti-slip control of the step motor drive 102. The desired speedsignals are delivered by the printer control 101.

To prepare a print process (start mode) following the startup of theprinter or the insertion of a new paper web, the following procedure isfollowed:

A paper web 5 is manually drawn into the printer through the variousassembly components up to the drive assembly 13. There, the front edge110 of the paper web 5 is threaded into the area of the rule 65 up tothe guide surface 67.

If the paper web 5 has margin perforation, this is brought into contactwith the spindles of the pin feed wheel 82 that has been pivoted in. Ifit paper web 5 does not have a perforation, the pin feed wheel 82 ispivoted into the out position.

In the area of the rule 65, the feed of the paper web 5 already occursvia the drive motor 41. The operator determines the direction of thefeed (forward/reverse) in order to align the beginning of a pageprecisely to a mark on the rule 65 that corresponds to the page length.The feed occurs relatively slowly and in small grid increments.

In the case of margin-perforated paper, the transport increments in thestart mode amount to only fractions of the hole grid spacing, whichtypically equals {fraction (1/6+L )} in. (approx. 4.3 mm). For example,the stepwidth equals {fraction (1/20+L )} grid spacings (approx. 0.21mm). In this mode of transport, the speed or position of the paper isdetected using the pin feed wheel sensor 85 and is compared to the speedor position of the drive motor.

A discrepancy between these two speeds or positions, for instance due toslippage, a crumpled paper web, or imprecisions in the drive rollers, isdetected in this way and is compensated by the drive control 100 byadditional advance (additional increments in the transport direction).

If paper without a margin perforation is used, the position and/or speedof the paper web 5 is scanned with the mark sensor 59, whose electroniccomponents 107 deliver corresponding signals to the drive control 100.Other sensors which are known per se besides the above described sensor50 can also be used to measure the speed, for instance the sensordescribed in DE 44 28 156 A1 or in U.S. Pat. No. 5,204,620.

The procedure for properly inserting and transporting the paper and forsensitizing the mark sensor is described below with the aid of the FIGS.5,6 and 7.

First, the paper web 5 is positioned approximately with its front edge110 in the area of the sensor 59, or respectively, of the rule 65. Theoperator is allowed a ceratin tolerance here of several millimeters, forexample, by which the position of the front edge (page beginning) of thepaper web 5 may deviate from the desired position. A correspondinginsertion mark 65 a is provided on the rule 65 for the desired position.Different insertion specifications are possible for this. For example,the insertion mark can be located at different points on the rule,depending on the page length. Alternatively, it can be provided that acommon insertion mark 65 a is provided on the rule 65 for different pagelengths. Finally the insertion marks can also be located directly underthe sensor 59; that is, at its scanning point (Step S1). The page lengthon which the blank is based is then inputted at the control panel 105 ofthe printer, and the value is stored in the memory 106 (Step S2).

From the forms that have been preprinted on the paper web, a particularitem of information is then selected, which is to serve as mark 109.Either this mark 109 can be an item of text or of graphic information,or it is possible to use an altered surface structure, for instance, awindow cutout that is punched into the forms. The sensor 59 is adaptedto the respectively selected mark information. In the presentexemplifying embodiment, an optoelectronic sensor 59 having a highcontrast sensitivity and a color sensitivity is used. If window cutoutswere to be used as mark information, a mechanical scanning device or anultrasound sensor could be suitable mark sensors. The item ofinformation of the form which is used as mark 109 should occur only onceper page of the form with respect to feed direction A. If the mark 109occurs several times on one page of the form, then the evaluationelectronics of the sensor 107, or respectively, the assembly control100, must be capable of filtering out the repetitions within the page,so that the drive can be controlled precisely to the page beginninginformation.

If characteristic attributes of the mark 109 are known, such as themagnitude of the contrast transition, color of the background, color ofthe mark information, and so on, these can also be input via the controlpanel 105 and stored in the memory 106 (step S3, S4).

The information indicating the region of the form in which the mark 109is located is also interrogated and stored, as warranted. A window inwhich the sensor responds to the mark information is thus defined withinthe form.

The specifying of a mark window also guarantees that the markinformation is allocated page-exactly even when one and the same mark109 occurs multiple times identically on one page of a form. The datatransfer between the control panel 105, the higher-ranking printercontrol 101, and the assembly control 100 occurs via the data bus 112.

The characteristic data about the mark can also be loaded by the printcontrol 101, to the extent that it receives this data from elsewhere.For example, the data can be co-delivered in the header region of aprint job (job). An operator who configures this print job on ahigher-ranking computer (print server) can add this information to theprint job at this stage, thereby automatizing the print process stillfurther once the print job comes in.

When the characteristic values of the mark are not known, an automaticprocedure 111 is set in motion, with which the assembly control 100detects and stores the characteristic values of the mark 109 fullyautomatically. This sensitizing process, as it is referred to, isdescribed more closely later in connection with FIG. 7.

Returning to FIG. 6, an incremental advance of the drive 13 occurs in avery small grid, which corresponds to {fraction (1/60+L )} of the holespacing of margin-perforated paper. In this phase, the actual pagelength of a form on the paper web 5 is determined. With each feedincrement (S5), a counter n is incremented by the value 1 (step S6), anda check is then performed as to whether the mark has been detected (stepS7). If not, an advance of one increment is again made, and the countern is again raised (steps S5, S6). If the mark has been detected, thepage length value is extracted from the memory 106, and an advance ofnearly one page length is performed; that is, an advance of a number ofincrements that is less than the number of increments of the page length(n_(s1)) by x (step S8).

Next, one increment is again advanced, respectively, and the incrementcounter n is raised by the value 1 (steps S9, S10). After this, it isagain checked whether the next mark has been detected (step S11); ifnot, an advance is performed again and the count raised; if so, then thevalue n is kept as the current page length value and is stored in thememory 106 (step S12). Next, a message “ready to print” is generated(S13). Before the print process can be started on the photoconductivedrum, the paper is positioned correctly with respect to thephotoconductive drum 16 using the previously acquired values for thepage length and the mark position.

By the method described, it is possible to compute both the preciseposition of the blank on the paper relative to the printing group andthe actual length of the form, which is important for paper transport.With the precise information about the position of the forms and aboutthe length of the forms, the print process can be started immediatelywith a highly precise fit.

To sensitize the sensor (FIG. 7), the sensor is first calibrated to thebackground of the paper web 5 in procedure 111. To accomplish this, theunprinted paper web is scanned by the sensor, and the sensor signals areread and temporarily stored (step S15). Next, it is checked whether thebackground information has a sufficiently large signal intensity (stepS16). If not, sensor parameters such as amplification, illuminationintensity, and so on, are modified, and step S15 is repeated until thesensor signals are sufficiently large. Next, the paper web 5 is movedforward in the recording direction (step S17) until the sensor detects asufficiently large mark that is distinguishable from the background(step S18). If a mark cannot be fixed with sufficient precision in apredetermined number of feed increments, then the paper web 5 iswithdrawn completely again, the settings at the sensor are changed, anda new search process is started. Here, the sensor settings are modifieduntil the sensor detects a mark. The search process can be aborted bythe user at any time. Besides the brightness of the light sources thatare integrated in the sensor, their spectral distribution (red, green,blue) can also be modified. In this way, colored marks on a coloredbackground can be reliably detected by the sensor. The computed valuesfor the background and the marks are stored in the memory 106 (stepS19). Following step S19, the start procedure is continued at step S8.For this purpose, an instructional command “return to main” is delivered(step S20).

During normal operation in which the print process in running, the paperweb 5 is processed page by page, with complete pages always beingprinted. Slippage between drive 13 and paper web 5 is detected in thismode in the same way as in the start mode, but is not compensated byadditional feed, but rather by a higher speed of the drive motor. Whenpaper with margin perforation is used, the margin holes are continuouslyscanned by the pin feed wheel sensor 85, and the scan signals are usedfor anti-slip control. When paper without margin perforation is used,the mark is scanned page by page, and this scan result is used foranti-slip control. This page-by-page scanning can be used instead of orin addition to the scanning of the pin feed wheel sensor even givenmargin-perforated paper. It is critical in this page-by-page controlvariant that the drive 13 is precise enough that there are noexcessively large shifts of the print format within a page at the pageends (or respectively, shortly before the mark of the next page).

If it is necessary to stop the printer from a running print operation,the drive control does not effectuate an immediate stop of the drive;but rather, a stop at the next page change. Because of this measure, theallocation of the increments of the drive motor to the scanned marks ismaintained very effectively.

When the print process is continued following a print stoppage, thedrive is first moved a few increments or even page lengths opposite theprint transport direction A and then accelerated in direction A. Theacceleration process can occur exactly corresponding to the movement ofthe start mode. Characteristic values related to the necessary feedcompensation are thus likewise stored in the start phase and can beutilized in the continuation of an interrupted print process.

What these measures accomplish is that the print operation can becontinued page-exactly following a print stoppage, and maculature isavoided. Since the page length of the paper web is known from the startoperation, its value can be used again following a print stoppage. Theprocedure for determining the page length (FIG. 6) can then be forgone.

If it is necessary to reinsert the paper web 5 following a printstoppage, for instance after a paper tear, the following procedure isfollowed: first, the operator positions the new paper web 5approximately in the insertion area 67 at the rule 65. Next, the paperweb 5 is transported forward by the drive assembly 13 at a first speed,which is slow, until the mark sensor 59 detects a mark. With the aid ofthis detected mark position and of the page length that was detectedbefore the print stoppage, the paper web 5 is again positioned in pageexactly fashion with respect to the printing station 14, and the printprocess is continued.

In a still improved embodiment of the start mode, following theidentification of two successive marks, the paper web is transportedrelative to the mark sensor back and forth between the detected marksonce or several times. In this way, dynamic conditions in theacceleration of the paper web 5 can be more precisely computed, and thedrive control in the acceleration phase can be improved still further.In particular, an optimal speed characteristic of the drive iscalculated, by means of which slippage is extensively compensated. Thesevalues can be stored for specific jobs or specific papers, respectively,and used for additional regulation of the drive speed in a continuationfollowing a print stoppage.

Using the signals of the paper width sensor 17, the drive control 100can also determine whether and what kind of paper has been inserted inthe printer. For this purpose, the drive motor is driven back and forthseveral times, and the sensor signals are evaluated. If one or moreholes are detected, a perforated paper web is assumed. An automaticaligning to the hole grid can then ensue with the aid of the detectedhole positions.

FIG. 8 shows different variants for sensitizing a mark sensor 59. In thevariant shown in FIG. 8a, the mark 109 is scanned using the mark sensor59 directly on the paper web 5. In the variant shown in FIG. 8b, areference measurement surface 30 is pivoted in front of the mark sensor59 instead of the mark, and this is scanned. The reference measurementsurface 30 corresponds to the mark 109 with respect to shape, coloringand/or other criteria. From the set of predetermined mark parameters, asuitable measurement surface which corresponds to the mark of a currentprint job can be selected from several measurement surfaces that havebeen stocked in the printer. The selection of the suitable measurementsurface can be controlled automatically by corresponding mark parametersthat are defined within the print job, or can be manually initiated bythe operator.

FIG. 8c shows a variation that corresponds to that described in FIG. 8b,although here, instead of the measurement surface 30 being moved infront of the mark sensor 59, the mark sensor 59 is pushed toward themeasurement surface 30. To determine the background of the mark, thepaper web 5 directly, or again a background measurement surface 31, canbe moved in front of the mark sensor in accordance with the variantrepresented in FIG. 8d. The contrast, which is needed in order to detectthe mark reliably, is determined from the measured values of the mark,or respectively, the mark measurement surface 30, and the value for thebackground. With the aid of this contrast value, correction parameterscan also be set at the sensor 59, so that this can detect the markreliably.

The determination of the mark parameters and/or of the contrast can beperformed by the print control completely automatically if themeasurement surfaces are positioned in front of the mark sensor with theaid of a drive, or if the sensor can be displaced automatically.

If a printed location of the paper were accidentally located in front ofthe sensor during the measurement of the background, such as the printformat 32 in FIG. 8f, a faulty measurement would take place. This wouldbecome manifest in a poor contrast ratio. The print control can thenmove the paper web 5 in or against the transport direction A and repeatthe measurement of the background at an unprinted location, asillustrated in FIG. 8g. The measurement result that delivers the bestcontrast ratio can then be used in the control process. In this method,it is not necessary that an operator positions both the unprinted paperand the preprinted mark immediately in front of the sensor and triggers,or respectively, performs the measurement. This facilitates andaccelerates the sensitizing of the sensor and thus shortens thepreparation time of the printer up to the start of printing. In theprocessing of a preprinted paper web, the operator can communicate thecolor of the preprinted mark to the printer system, for example. Theprint control can then immediately perform the sensitization(measurement) of the sensor to the paper web that is to be processed, orrespectively, to the mark that is located on it, using a suitablemeasurement surface.

FIG. 9 shows two examples of measurement surfaces, the measurementsurface 33 being constructed linear and reproducing several segmentswith various shades of gray and/or colors. The measurement surface 34has exactly such segments, as well as a void 35, which is provided forthe scanning of the paper web 5 or the background measurement surface31.

FIG. 10a shows a first variation for determining the contrast on a paperweb 5. A measurement surface 35 that is covered by a gray grid isprinted on the paper web 5 by a first printer 37 and transported to asecond printer 38. There, the mark sensor 59 scans the paper web 5.First, the sensor 59 scans the unprinted paper web 5 and stores themeasured brightness background. Then the paper web 5 is transported fromthe first printer 37 to the second printer 38 until the measurementsurface 35 is situated in front of the mark sensor 59 in the secondprinter 38. There, the brightness value of the printed surface 35 ismeasured, and the contrast of the bright (unprinted) surface and dark(printed) surface is stored. Lastly, the print control checks whetherthe contrast obtained is sufficient. If not, the sensitization processis repeated again, with the sensor parameters being set at greatersensitivity and/or the mark being printed again with a greaterthickness, and with the initialization process being repeated.

In the variation shown in FIG. 10b, an additional user intervention isrequired, though this does not require the insertion of unprinted paperin the second printer for the determination of the background value.

In the method represented in Fig. 10b, the first printer 37 prints astripe pattern 36 on the paper web 5. At the same time, the secondprinter 38 advances the paper web 5 by the same length without printing,until the printed region is situated in the region of the mark sensor59. The second printer 38 then positions the paper web so that anunprinted surface of the stripe pattern 36 is situated in front of themark sensor 59. The brightness value of the unprinted paper is stored inthis process. Next, the second printer 38 positions the paper web suchthat one of the previously printed stripes of the stripe pattern 36 issituated in front of the mark sensor 39. The second step of thesensitizing process is then performed: the brightness value of theprinted paper is measured, and finally the contrast of bright and darksurfaces is stored. Lastly, it is rechecked whether the obtainedcontrast value is sufficient, or the measurement is repeated at othermeasurement positions, as warranted, until a sufficiently high contrastis achieved.

The printing of a gray grid in accordance with FIG. 10a can also be usedto optimize the scanning surface of the mark sensor. As can be seen inFIG. 11a, the annular scanning surface 39 of the sensor 59 can detect agray area 22. If black marks that do not cover the entire scanningsurface of the sensor are printed in the print operation, in accordancewith the embodiment 21 in FIG. 11b, then the brightness of the thin,line-shaped mark 21 that is detected by the sensor is approximatelycomparable to the brightness value of the gray surface of FIG. 11a. Thescanning accuracy in the print operation is thus greater when a graysurface is used for the teach-in process instead of a black one. This isparticularly advantageous when very narrow black lines are used in theprint operation, which would hardly be possible to position withsufficient exactness during the teach-in process.

Although the invention was described primarily using exemplifyingembodiments that utilize paper as the recording medium, it can also ofcourse be applied in connection with other recording media, such asfilms. It is also not bound to a specific imaging means such asphotoconductive drums, but can be utilized in connection withband-shaped transmission media such as photoconductive tapes ormagnetographic means. Finally, the invention can be applied to printersbased on other recording principles, for instance ink-jet printers orthermotransfer printers.

By providing several control marks on a page of a form, it would bepossible to increase the control precision within a page formargin-perforated paper as well. Finally, using a motor drive which actson the mark sensor transverse to the paper transport direction(direction E in FIG. 5) in the start mode, the sensor could detect themarks in this direction in space automatically. The automatization leveland thus the operative reliability could thus be further increased.

An additional automatization can be achieved when the mark sensor 59 isdisplaced by motor along its axle 73 in direction E for itssensitization (FIG. 3).

Although various minor changes and modifications might be proposed bythose skilled in the art, it will be understood that our wish is toinclude within the claims of the patent warranted hereon all suchchanges and modifications as reasonably come within our contribution tothe art.

What is claimed is:
 1. A method for controlling a drive assembly in anelectrographic printer which transports a web-shaped recording mediumthat has been preprinted in pages, comprising the steps of: selecting arecording medium which has been preprinted with information arbitrarilyin pages; scanning the recording medium continuously by a sensor duringprint operation; selecting a regularly recurring mark from thepreprinted information or from a surface structure of the recordingmedium; sensitizing the sensor to the regularly recurring mark of therecording medium by setting sensor parameters; and regulating atransport speed of the recording medium using scanned sensor signals. 2.The method according to claim 1 wherein the mark is selected from thepreprinted information of the recording medium.
 3. The method accordingto claim 1 wherein for the sensitizing, at least one referencemeasurement surface is scanned which is not printed on the recordingmedium and which corresponds to the mark with respect to parameters thatare to be scanned.
 4. The method according to claim 3 wherein thereference measurement surface is optionally pivotable within the printerto a position in front of the sensor.
 5. The method according to claim 3wherein a second reference measurement surface is scanned whichcorresponds to unprinted recording medium.
 6. The method according toclaim 5 wherein a contrast value is computed from the scanning of thetwo reference measurement surfaces.
 7. The method according to claim 1wherein an opto-electronic sensor is used.
 8. The method according toclaim 1 wherein the mark is located in a print-capable area of theprinter.
 9. The method according to claim 1 wherein a surface structurein a form of a window cutout is used as the mark.
 10. The methodaccording to claim 1 wherein the mark is applied page by page.
 11. Themethod according to claim 1 wherein to sensitize the sensor, first abackground of the recording medium is scanned, and then the mark isscanned.
 12. The method according to claim 1 wherein the sensor issensitized spectrally.
 13. The method according to claim 1 wherein forthe sensitizing and/or to detect the marks following a first markdetected, the recording medium is transported with a predeterminedspeed; a window is prescribed within which sensor signals are detected,in particular a time window or a number of steps of a step motor ischecked to determine whether the mark is detected within this window;and an error message is output when the mark is not detected within thetime window.
 14. The method according to claim 1 wherein for thesensitizing, a start area of the recording medium is seated at apredetermined starting position in the printer; and a drive assemblytransports the recording medium from the starting position in atransport direction.
 15. The method according to claim 1 wherein afriction drive is used as a drive assembly for the recording medium. 16.The method according to claim 1 wherein the mark is detected by thesensor page by page.
 17. The method according to claim 1 wherein acontrol that is allocated to the sensor is used to which characteristicdata about the mark is fed.
 18. The method according to claim 17 whereinthe characteristic data contain location information and/or spectralinformation.
 19. The method according to claim 1 wherein the recordingmedium is first moved a specific length in a recording direction inorder to sensitize the sensor to a specific mark, and it is moved in anopposite direction if the mark was not found during forward motion. 20.The method according to claim 19 wherein following an unsuccessfulsearch for the marks in a predetermined area of the recording medium,sensor parameters are modified, and a new search for the mark isexecuted.
 21. The method according to claim 1 wherein a sensor isprovided whose coverage area can be modified transverse to a transportdirection of the recording medium.
 22. The method according to claim 1wherein a sensor is used which is mounted such that it is displacedtransverse to a transport direction, namely one which is motor-driven.23. The method according to claim 1 wherein a camera that has topicalresolution and that covers an entire width of the recording medium isutilized as the sensor, an evaluation range of the camera being limited.24. The method according to claim 1 wherein a spectrally sensitizablesensor is used; and that input and/or a storage unit are used with aidof which a control unit of the sensor is fed mark-specific data.
 25. Themethod according to claim 1 wherein several cycles of forward-reversemovements are executed, an adjustment value at the sensor being modifiedfollowing each cycle.
 26. A method for controlling a drive assembly inan electrographic printer which transports a web-shaped recordingmedium, comprising the steps of: selecting a recording medium which hasbeen preprinted with information in pages; scanning the recording mediumby a sensor during print operation; selecting a recurring mark from thepreprinted information or from a surface structure of the recordingmedium; sensitizing the sensor to the recurring mark of the recordingmedium by setting at least one sensor parameter; and regulating atransport speed of the recording medium using scanned sensor signals.27. A device for controlling a drive assembly in an electrographicprinter which transports a web-shaped recording medium that has beenpreprinted in pages, comprising: a sensor which scans the recordingmedium for regularly recurring marks and which scans the recordingmedium continuously during print operation; a control device whichregulates a transport speed of the recording medium using scan signalsof the sensor; a selection device with which a regularly recurring markis selected from the recording medium which has been arbitrarilypreprinted in pages; and a sensitizing device by which the sensor issensitized to the regularly recurring mark by setting of sensorparameters.
 28. A printing system, comprising: a first printer and asecond printer which print a web-shaped recording medium in succession,in which a mark that is made on the recording medium by the firstprinter is scanned in the second printer, and a result of the scan isutilized to control a drive assembly; the web-shaped recording mediumbeing preprinted in pages; a sensor which scans the recording medium forregularly recurring marks and which scans the recording mediumcontinuously during print operation; a control device which regulates atransport speed of the recording medium using scan signals of thesensor; a selection device with which a regularly recurring mark isselected from the recording medium which has been arbitrarily preprintedin pages; and a sensitizing device by which the sensor is sensitized tothe regularly recurring mark by setting of sensor parameters.
 29. Adevice for controlling a drive assembly in an electrographic printerwhich transports a web-shaped recording medium, comprising: a sensorwhich scans the recording medium for recurring marks and which scans therecording medium during print operation; a control device whichregulates a transport speed of the recording medium using scan signalsof the sensor; a selection device with which a recurring mark isselected from the recording medium which has been preprinted in pages;and a sensitizing device by which the sensor is sensitized to theregularly recurring mark by setting of at least one sensor parameter.